Request based collation fetching (#2621)

* Introduce collation fetching protocol

also move to mod.rs

* Allow `PeerId`s in requests to network bridge.

* Fix availability distribution tests.

* Move CompressedPoV to primitives.

* Request based collator protocol: validator side

- Missing: tests
- Collator side
- don't connect, if not connected

* Fixes.

* Basic request based collator side.

* Minor fix on collator side.

* Don't connect in requests in collation protocol.

Also some cleanup.

* Fix PoV distribution

* Bump substrate

* Add back metrics + whitespace fixes.

* Add back missing spans.

* More cleanup.

* Guide update.

* Fix tests

* Handle results in tests.

* Fix weird compilation issue.

* Add missing )

* Get rid of dead code.

* Get rid of redundant import.

* Fix runtime build.

* Cleanup.

* Fix wasm build.

* Format fixes.

Thanks @andronik !

polkadot/Cargo.lock

@@ -96,6 +96,12 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "always-assert"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fbf688625d06217d5b1bb0ea9d9c44a1635fd0ee3534466388d18203174f4d11"
+
 [[package]]
 name = "ansi_term"
 version = "0.11.0"
@@ -5322,10 +5328,10 @@ dependencies = [
 name = "polkadot-collator-protocol"
 version = "0.1.0"
 dependencies = [
+ "always-assert",
  "assert_matches",
  "env_logger 0.8.2",
  "futures 0.3.12",
- "futures-timer 3.0.2",
  "log",
  "polkadot-node-network-protocol",
  "polkadot-node-primitives",
@@ -5649,8 +5655,6 @@ dependencies = [
  "polkadot-primitives",
  "sc-network",
  "strum",
- "thiserror",
- "zstd",
 ]
 
 [[package]]
@@ -5845,6 +5849,8 @@ dependencies = [
  "sp-std",
  "sp-trie",
  "sp-version",
+ "thiserror",
+ "zstd",
 ]
 
 [[package]]